Gas turbine engines are often used to power aircraft and to supply industrial power. A gas turbine engine includes, for example, four major sections: compressor, combustor, turbine, and exhaust.
The compressor section raises the pressure of the air to a relatively high level. Compressor components such as compressor blades and impellers are primary components in this cold section for any turbine engine. The compressed air from the compressor section then enters the combustor (hot) section, where a ring of fuel nozzles injects a steady stream of fuel. The injected fuel is combusted by a burner, which significantly increases the energy of the compressed air.
The high-energy compressed air from the combustor section then flows into and through the turbine section, causing rotationally mounted turbine blades to rotate and generate mechanical energy. Specifically, high-energy compressed air impinges on turbine vanes and turbine blades, causing the turbine to rotate. Rotation speeds greater than 39,000 rpm are common. The turbine includes one or more shafts that are used to drive a generator for supplying electrical power, and to drive its own compressor and/or an external load compressor. The air exiting the turbine section is exhausted from the engine via the exhaust section.
Ingestion of microscopic particles, e.g., dust, that is entrained in incoming engine air flow poses one of the most significant limitations to turbine engine durability. A small portion of the engine airflow is routed through cooling passages in the turbine blades and nozzles, where accumulation of particles over time can block the cooling air flow and cover the surfaces with an insulating particle layer that reduces cooling effectiveness. Additionally, any corrosive substances in the particles may chemically react with the base alloy at the high turbine operating temperatures, thereby corroding the surfaces. Over time, continued particle accumulation can lead to failure of the turbine blades and vanes. The most common symptom of such component failure is a large performance decrease, resulting in premature removal of the engine for low power output. Occasionally, symptoms are not observed until there is a failure of the turbine with extensive secondary damage to the engine resulting high repair cost.
The effects of turbine damage due to particle ingestion are of particular concern in turbine engines that operate for significant periods in dusty or polluted near-ground environments, for example, auxiliary power units (APU's), ground vehicle engines, and military helicopter engines. Traditional approaches to prevent particle ingestion damage include maintenance only or particle separation at the engine inlet.
Many engines have no devices to mitigate the effects of particle ingestion, and rely only on engine maintenance. The consequences of particle ingestion are dealt with through engine removal and repair when the engine shows symptoms of functional impairment. In high-risk applications, proactive engine removal may be accomplished at prescribed intervals after first use or after the previous engine overhaul. These approaches are inherently expensive as they allow turbine deterioration to proceed unimpeded, resulting in frequent replacement of high-cost turbine components, and more extensive replacement of engine components in cases of catastrophic turbine failures with widespread secondary damage.
Devices may be installed at the engine inlet to remove particle from incoming air. Such devices fall into two categories: inertial particle separators and inlet barrier filters.
Inertial particle separators rapidly turn the engine incoming airflow at the engine air inlet, with the intent that the inertia of incoming particles causes them to continue in a straight path, being unable to negotiate the sharp turns of the main airflow into the core of the engine. The particles are then eliminated from the system by a scavenge blower that draws its incoming air from the region of particle accumulation. The sharp turn of incoming air is accomplished either by a sudden sharp inward turn into the engine core with scavenge flow drawn from the outer wall, or in an array of vortex tubes having spiral-shaped fins which spin the incoming air and scavenge the particle from the outer walls of the tubes. These inertial particle separators can process large amounts of air with minimal pressure loss, while removing most large particles from the incoming air flow. However, these separators may allow considerable amounts of the smaller particles to enter the engine core.
Inlet barrier systems use a filter that mechanically traps incoming particles. The barrier systems can offer very high separation efficiencies down to the smallest particles, depending on the design of the filter. However, the barrier systems present a considerable resistance to the incoming air flow which reduces engine performance. This resistance increases as the barrier becomes clogged with particles over time. Recurring maintenance is needed for cleaning or replacement of the filter. The large filter surface area needed to pass the entire engine inlet airflow without large performance decrements typically results in very large inlet hardware.
These known engine inlet particle separation systems, while reducing the rate of turbine deterioration due to particle ingestion, add considerable cost and weight to the engine. They are bulky and are difficult to integrate the engine into the aircraft or vehicle, and pose an overall performance loss due to either the energy needed to drive the scavenge blower or the inlet pressure loss of a barrier filter. The performance loss of an inlet particle separation system is manifested as either, or a combination of reduced power output, increased fuel consumption, and increased turbine operating temperature (which accelerates turbine deterioration).
Other known methods to reduce particle damage include using the rotation of the rotor and the centrifugal force thereby created to separate the particle from the airflow. See for example, U.S. Pat. Nos. 3,673,771, 3,918,835, and 4,309,147. However, enhanced dust separation over these existing devices is needed.
Accordingly, it is desirable to provide a method and apparatus for removing particles from the airflow prior to reaching the turbine blades. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.